Every one that I have ever shot (3-4) eventually needed bedding. They were all 7mag or 300WM so there was some serious recoil issues. The first 100-150 rounds were all pretty accurate but overtime the Aluminum block began to loosen. Well lets just say the fit wasnt as tight. I could tell because the guns would begin to shoot two separate groups. Shots 1,3,5,7 ect were together and shots 2,4,6,8 were together. Usually about 1MOA apart.

Not a ton of experience but my 2cents

You just touched on a reason that McMillan doesn't use Aluminum Bedding blocks in their rifles.

However, if you do a good bedding job straight from the start, especially getting a good seat at the recoil lug it will never be a problem.

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